Pyrophosphate-containing bath for cyanide-free deposition of copper-tin alloys

ABSTRACT

A pyrophosphate-containing bath for the cyanide-free deposition of copper alloys on substrate surfaces, comprising a reaction product of a secondary monoamine with a diglycidyl ether, is described. The electrolyte bath is suitable for the galvanic deposition of glossy white, even and uniform copper-tin alloy coatings.

FIELD OF THE INVENTION

The invention relates to a pyrophosphate-containing bath for thecyanide-free deposition of copper-tin alloys on substrate surfaces,which comprises a reaction product of a secondary monoamine with adiglycidyl ether as additive.

Homogenous, glossy copper-tin alloy layers, the alloy ratio of which maybe directly adjusted depending on the used metal salt ratio within theelectrolyte, may be cyanide-freely deposited by the bath.

PRIOR ART

Tin alloys and particularly copper-tin alloys as alternative for nickeldepositions have become the focus of attention. Galvanically depositednickel layers are usually used not only for decorative but also forfunctional applications.

Despite their good properties, nickel layers are problematic as regardshealth, particularly regarding direct skin contact, due to theirsensibilising properties. Therefore, alternatives are of greatestinterest.

Besides the tin-lead alloys, which are established in the sector ofelectronics but ecologically problematic, copper-tin alloys have beentaken into consideration as replacement in the last few years. Chapter13 (pp. 155 to 163) of the document “The Electrodeposition of Tin andits Alloys” by Manfred Jordan (Eugen G. Leuze Publ., 1st ed., 1995)gives a review on the known types of baths for copper-tin alloydepositions.

Cyanide-containing copper-tin alloy baths are industrially established.Due to regulations that become more and more stricter and the hightoxicity and the problematic and expensive disposal of thesecyanide-containing baths, there is an increasing need for cyanide-freecopper-tin electrolytes.

For this purpose cyanide-free pyrophosphate-containing electrolytes havebeen sporadically developed. JP 10-102278 A describes a copper-tin alloybath on pyrophosphate basis, which contains a reaction product of anamine and a epihalodrine derivative (molar ratio 1:1), an aldehydederivative and optionally, depending on the application, tensides asadditive. U.S. Pat. No. 6,416,571 B1 also describes apyrophosphate-based bath, which also contains a reaction product of anamine and an epihalohydrine derivative (molar ratio 1:1), a cationictenside, optionally further surface-active tensides and an antioxidantagent as additives.

The disadvantage of the above-mentioned baths is that particularly asregards drum plating, no uniform alloy layers are obtained, so that theproducts have no uniform colouring and gloss.

To solve this problem, WO 2004/005528 suggests apyrophosphate-containing copper-tin alloy bath that contains a reactionproduct of an amine derivative, particularly preferred piperazine, of anepihalohydrine derivative, particularly epichlorhydrine, and of aglycidyl ether as additive. To produce this reaction mixture, a mixtureconsisting of epichlorhydrine and the glycidyl ether is slowly added toan aqueous solution of the piperazine under precise temperature control,whereby the temperature of 65 to 80° C. has to be kept. The disadvantageof this additive is the reaction procedure that is difficult to control,particularly at high temperatures, since such reaction products tend topost-reaction at too high reaction temperatures and/or storagetemperatures and, thus, to the formation of high-molecular and, thus,partially water-insoluble and ineffective polymers. One way out of thisdilemma may only be achieved by a reaction procedure in very highdilution (<1% by weight). Such low concentrated additive solutionsresult in a disadvantageous solution formation of the electrolyte ifseveral doses are added. This may result in fluctuating depositions ifthe electrolyte is used for a longer period of time.

Moreover, this electrolyte shows weaknesses as regards applications inthe rack plating. For example, the quality of the deposited layers,which often show a haze, very strongly depends on the way of movement ofgoods during the electrolysis. Furthermore, the thus obtained copper-tincoatings often show porosities, which is particularly problematicregarding decorative coatings.

Example A-11 on page 26 of WO 2004/005528 describes the use of areaction product of the diamine piperazine with ethylene glycoldiglycidyl ether. This reaction product only provides dull white-bronzelayers.

SUMMARY OF THE INVENTION

Therefore, it is the objective of the invention to develop a galvanicbath for copper-tin alloys, which enables the production of opticallyappealing copper-tin alloy layers.

A more homogenous copper-tin alloy metal distribution and an optimalcopper/tin metal ratio are to be additionally adjusted. Moreover, auniform layer thickness with high gloss and the regularity of thedistribution of the alloy components in the coating are to be maintainedover a large current density range.

The subject-matter of the invention is a pyrophosphate-containing bathfor the cyanide-free deposition of copper alloys on substrate surfacescomprising a reaction product of a secondary monoamine with a diglycidylether.

The secondary monoamines and the diglycidyl ethers may thereby be usedindividually or in mixture to produce the reaction product.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Preferred secondary amines are dimethylamine, diethylamine,dipropylamine, dibutylamine, dipentylamine, diisoproylamine, piperidine,thiomorpholine, morpholine and mixtures thereof. Particularly preferredis the use of morpholine. Particularly preferred diglycidyl ethers areglycerol diglycidyl ether, poly(ethylene glycol) diglycidyl ether,poly(propylene glycol) diglycidyl ether and their mixtures.

A particularly preferred reaction product for use in the bath accordingto the invention is the reaction product of morpholine with glyceroldiglycidyl ether.

The organic additives may be easily depicted by reacting the respectiveamine components with the respective diglycidyl ethers in an appropriatesolvent such as, e.g., water, aqueous alcoholic solutions, aproticsolvents such as, e.g., ethers, NMP, NEP, DMF, DMAc or also in substanceat room temperature or in heat under standard pressure or increasedpressure. Regarding the production in substance, it is purposeful todilute the reaction product with water after the end of the reaction.The reaction times needed therefor are between a few minutes and severalhours, depending on the ingredient used. Besides the classic heatsources, a microwave oven may also be used here. In the case of the useof water as solvent or the production in substance, the resultantreaction products may be used directly, so that a production in aqueousmedium or in substance is the preferred manufacturing process. Thepreferred temperatures of the production of the reaction productsaccording to the invention are 15 to 100° C., particularly preferred 20to 80° C. The molar ratios of diglycidyl ether/amine are 0.8 to 2,particularly preferred 0.9 to 1.5. Compared to the additive of WO2004/005528, the very simple production is particularly advantageousregarding these additives.

The reaction products according to the invention may be usedindividually or as mixture of several different reaction products of theaforementioned type in a concentration of 0.0001 to 20 g/l, preferably0.001 to 1 g/l and particularly preferred 0.01 to 0.6 g/l.

According to a preferred embodiment, the bath according to the inventioncontains orthophosphoric acid, an organic sulfonic acid, boric acid, anantioxidant agent and an organic brightener that is different from thereaction product.

The electrolyte baths according to the invention may contain copperpyrophosphate in a concentration of 0.5 to 50 g/l as copper ion source,whereby concentrations of 1 to 5 g/l are particularly preferred.

The baths according to the invention may contain tin pyrophosphate in aconcentration of 0.5 to 100 g/l as tin-ion source, wherebyconcentrations of 10 to 40 g/l are particularly preferred.

Besides the aforementioned tin pyrophosphates and copper pyrophosphates,other water-soluble tin salts and copper salts may also be used such as,e.g. tin sulfate, tin methanesulfonate, copper sulfate, coppermethanesulfonate, which may be re-complexated by adding appropriatealkali metal pyrophosphates to the respective pyrophosphates within theelectrolyte. The concentration ratio of pyrophosphate to tin/copper isthereby to be 3 to 80, particularly preferred 5 to 50.

The alkali metal pyrophosphates that might be contained in the bathsaccording to the invention are particularly preferably the sodiumpyrophosphates, potassium pyrophosphates and ammonium pyrophosphates inconcentrations of 50 to 500 g/l, particularly preferred of 100 to 400g/l.

The antioxidant agents that might be contained in the baths according tothe invention comprise hydroxylated aromatic compounds such as, e.g.,catechol, resorcinol, brenzcatechin, hydroquinone, pyrogallol,α-naphthol, β-naphthol, phloroglucin, and sugar-based systems such as,e.g., ascorbic acid, sorbitol, in concentrations of 0.1 to 1 g/l.

Monosulfonic acids as well as polysulfonic acids such as, e.g.,methanesulfonic acid, methanedisulfonic acid, ethanesulfonic acid,propanesulfonic acid, 2-propanesulfonic acid, butanesulfonic acid,2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid,decanesulfonic acid, dodecanesulfonic acid as well as their salts andtheir hydroxylated derivatives may be used as alkylsulfonic acids.Particularly preferred is the use of methanesulfonic acid in aconcentration of 0.01 to 1 g/l.

The baths according to the invention have a pH value of 3 to 9,particularly preferred 6 to 8.

As opposed to the additives known from WO 2004/005528, the additiveaccording to the invention, i.e., the reaction product of a secondarymonoamine with a diglycidyl ether, makes it possible to deposit thealloy on the substrate with a uniform layer thickness with high gloss atregular distribution of the alloy components in the coating over a largecurrent density range. Moreover, the use of the additive according tothe invention does not result in the formation of pores. Finally,fogging may be avoided in rack plating.

The aforementioned effects may even be increased by addingN-methylpyrrolidone. The N-methylpyrrolidone is preferably used in aconcentration of 0.1 to 50 g/l, particularly preferably 0.5 to 15 g/l.

The baths according to the invention may be produced by common methods,for example, by adding the specific amounts of the above-describedcomponents to water. The amount of the base components, acid componentsand buffer components such as, e.g., sodium pyrophosphate,methanesulfonic acid and/or boric acid, should preferably be selected insuch a way that the bath attains the pH range of at least 6 to 8.

The baths according to the invention deposit an even and ductilecopper-tin alloy layer without discolouration at each usual temperatureof about 15 to 50° C., preferably 20° C. to 40° C., particularlypreferably 20° C. to 30° C. At these temperatures the baths according tothe invention are stable and effective over a wide, set current densityrange of 0.01 to 2 A/dm², particularly preferably 0.25 to 0.75 A/dm².

The baths according to the invention may be operated in a continuous orintermittent way, and the components of the bath will have to be amendedfrom time to time. The components of the bath may be added individuallyor in combination. Moreover, they may vary over a wide range, dependingon the consumption and the present concentrations of the individualcomponents.

Table 1 shows, according to a preferred embodiment, the depositionresults of the tin-copper alloy layers in the electrolytes according tothe invention compared to the electrolytes of document WO 2004/005528.

appearance concentration used of the charge electrolyte brightener[ml/l] deposition 1 electrolyte according to the invention 0.2 veryglossy white with additive A (Preparation and Ap- deposition plicationExample 1) 2 electrolyte according to 0.5 grey dull deposition WO2004/005528 (Comparative with low adhesion Example 11, additive conc.:10% by weight 3 electrolyte according to 14 glossy white deposi- WO2004/005528 (Comparative tion with isolated Example 12, additive conc.:1% by pores and fogs weight)

As evident from Table 1, better results as regards appearance and theeffective concentration are obtained if the additives according to theinvention are used. Thus, the additives according to the invention aremore active by the factor of up to 1.75 than the additives described inthe patent specification WO 2004/005528.

Compared to the electrolytes of WO 2004/005528, one advantage of thetin-copper baths according to the invention is the surprisingly lowconsumption of the additives according to the invention compared to thereaction products of the piperazine with epichlorhydrine and glycidylether.

Generally, the aqueous baths according to the invention may be used forall types of substrates on which copper-tin alloys may be deposited.Examples of purposeful substrates include copper-tin alloys, ABS plasticsurfaces coated with chemical copper or chemical nickel, mild steel,high-grade steel, spring steel, chromium steel, chromium-molybdenumsteel, copper and tin.

Therefore, a further subject-matter is a method for galvanic depositionof copper-tin alloys on usual substrates, whereby the bath according tothe invention is used. The substrate to be coated is thereby introducedinto the electrolyte bath.

The deposition of the coatings in the method according to the inventionpreferably takes place at a set current density of 0.25 to 0.75 A/dm² aswell as at a temperature of 15 to 50° C., preferably 20 to 30° C.

The method according to the invention may be conducted in theapplication for mass production components, for example, as drum platingmethod and for the deposition on larger workparts as rack platingmethod. Anodes that may be soluble are thereby used such as, forexample, copper anodes, tin anodes or appropriate copper-tin alloyanodes, which are used as copper ion source and/or tin ion source at thesame time, so that the copper and/or tin that is deposited on thecathode is substituted by dissolution of copper and/or tin at the anode.

On the other hand, insoluble anodes (e.g., platinated titanium mixedoxide anodes) might be used, whereby the copper ions and tin ions thatwere detracted from the electrolyte have to be added again in anotherway, e.g., by adding the corresponding soluble metal salts. As it ispossible in the galvanic deposition, the method according to theinvention may be operated under nitrogen injection or argon injection,with movement of goods or without movement, without resulting in anydisadvantages for the obtained coatings. To avoid or reduce oxidationsof the added additives or the tin(II) ions, it may be worked with theseparation of the electrode rooms or with the use of membrane anodes,whereby a substantial stabilisation of the electrolyte may be achieved.

Commercially available continuous current rectifiers or pulse rectifiersare used as current source.

EXAMPLES Preparation Example 1

4 g (0.0455 mol) morpholine and 9.29 g (0.0455 mol) glycerol diglycidylether are dissolved in 19.84 g water in a round bottom flask, and thereaction mixture is heated to 80° C. for one hour. 33.13 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Preparation Example 2

1.67 g (0.0190 mol) morpholine and 10 g (0.0190 mol) poly(ethyleneglycol) diglycidyl ether (molecular weight 526.6 g/mol) are dissolved in17.44 g water in a round bottom flask, and the reaction mixture isheated to 80° C. for one hour. 29.11 g of a colourless liquid areobtained, which is subsequently used for application-technologicaltests.

Preparation Example 3

2.50 g (0.0287 mol) morpholine and 2.92 g (0.0143 mol) glyceroldiglycidyl ether and 7.53 g (0.0143 mol) poly(ethylene glycol)diglycidyl ether are dissolved in 19.43 g water in a round bottom flask,and the reaction mixture is heated to 80° C. for one hour. 32.38 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Preparation Example 4

1.67 g (0.019 mol) morpholine and 12.16 g (0.019 mol; average molecularweight: 640 g/mol) poly(propylene glycol) diglycidyl ether are dissolvedin 15.28 ml water in a round bottom flask, and the reaction mixture isheated to 80° C. for one hour. 21.22 g of a liquid are obtained, whichis subsequently used for application-technological tests.

Preparation Example 5

4.97 g (0.0472 mol) thiomorpholine and 9.64 g (0.0472 mol) glyceroldiglycidyl ether are emulsified in 21.92 g water in a round bottomflask, and the reaction mixture is heated to 80° C. for two hours. Afterthe end of the reaction, a yellow oil deposits. 23.60 ml 2-molarhydrochloric acid are added to the reaction mixture and stirred for 30minutes. 58.15 g of a yellow colourless liquid are obtained, which issubsequently used for application-technological tests.

Preparation Example 6

4.90 ml (0.0490 mol) piperidine and 10 g (0.0490 mol) glyceroldiglycidyl ether are dissolved in 15 g water in a round bottom flask,and the reaction mixture is heated to 80° C. for two hours. 35.43 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Preparation Example 7

6.20 ml (0.0490 mol) dimethylamine and 10 g (0.0490 mol) glyceroldiglycidyl ether are dissolved in 15 g water in a round bottom flask,and the reaction mixture is heated to 80° C. for two hours. 30.52 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Preparation Example 8

5 g (0.0574 mol) morpholine and 10 g (0.0490 mol) glycerol diglycidylether are dissolved in 22.50 g water in a round bottom flask, and thereaction mixture is heated to 80° C. for one hour. 37.50 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Preparation Example 9

5.69 g (0.0653 mol) morpholine and 10 g (0.0490) glycerol diglycidylether are dissolved in 23.54 g water in a round bottom flask, and thereaction mixture is heated to 80° C. for one hour. 39.23 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Preparation Example 10

4 g (0.0455 mol) morpholine and 9.29 g (0.0455 mol) glycerol diglycidylether are dissolved in 19.84 water in a round bottom flask, and thereaction mixture is heated to 60° C. for one hour. 33.13 g of acolourless liquid are obtained, which is subsequently used forapplication-technological tests.

Comparative Preparation Example 11 According to WO 2004/005528

131.65 ml (0.250 mol) poly(ethylene) diglycidyl ether are charged in around bottom flask, and 19.75 ml (0.250 mol) epichlorhydrine are addeddropwise while stirring within 15 minutes and are stirred for further 15minutes. This solution is slowly added dropwise to a solution of 21.535g piperazine in 75 ml water within one hour, without cooling, whilestirring strongly. Due to the addition a temperature of 80° C. isobtained, which is not to be exceeded. After the end of the addition,the reaction mixture is stirred for another hour at 80° C., whereby avery viscous solution was obtained. The reaction batch is cooled to roomtemperature and diluted with 229.81 g water. 500 g solution (40% byweight) were obtained, which reacted after a quarter of an hour. Thissolid mass was disintegrated by means of the Ultra-Turrax stirrer andadjusted to a 10% by weight polymer emulsion by adding more water. Theadditive was tested analogously to the General Example of Application.

Comparative Preparation Example 12 According to WO 2004/005528

3.3 ml (0.00625 mol) polyethylene glycol) diglycidyl ether are chargedin a round bottom flask, and 0.5 ml (0.00625 mol) epichlorhydrine areadded dropwise while stirring within 15 minutes and stirred for further15 minutes. This solution is slowly added dropwise to a solution ofpiperazine (0.55 g (0.00625 mol)) in 75 ml water at 80° C. within onehour, without cooling, while stirring strongly. After the end of theaddition, the reaction mixture is stirred for another hour at 80° C.,whereby a very viscous solution was obtained. The reaction batch iscooled to room temperature and diluted with 420 g water. 500 g solution(<1% by weight) were obtained. The additive was tested analogously tothe General Example of Application.

General Example of Application

An electrolyte with the following composition is used:

300 g/l tetrapotassium pyrophosphate 3 g/l copper pyrophosphatemonohydrate 30 g/l tin pyrophosphate 40 ml/l methane sulfonic acid 70%12.5 ml/l phosphoric acid 85% 4 ml/l N-methyl pyrrolidone 0.2 ml/l of a40% solution of one of the additives according to the invention inaccordance with one of the additives of Preparation Examples 1 to 10.

250 ml of the electrolyte with a pH value of 7 are filled into a Hullcell. A titanium mixed oxide electrode is used as anode. The cathodeplate is coated at 1 A for 10 min. After the end of the coating, theplate is rinsed and dried under compressed air. A glossy deposition wasobtained.

TABLE 2 molar ratio Preparation diglycidyl diglycidyl charge Exampleamine ether 1 ether 2 appearance 1 1 1 1 very glossy white deposition 22 1 1¹ glossy white deposition 3 3 1 0.5 0.5 glossy white deposition 4 41 1² glossy white deposition 5 5 1³ 1 glossy white deposition 6 6 1⁴ 1glossy white deposition 7 7 1⁵ 1 glossy white deposition 8 8 1.17 1 veryglossy white deposition 9 9 1.33 1 very glossy white deposition 10 10⁶ 11 very glossy white deposition 11 Compar- 1⁷ 1⁸ grey dull ativedeposition Example with low 11 adhesion 12 Compar- 1⁷ 1⁸ glossy whiteative deposition with Example isolated pores 12 and fogs ¹poly(ethyleneglycol) diglycidyl ether; ²poly(propylene glycol) diglycidyl ether;³thiomorpholine; ⁴piperidine; ⁵dimethylamine; ⁶production at 60° C.;⁷piperazine; ⁸poly(ethylene glycol) diglycidyl ether-epichlorhydrineadduct

1-25. (canceled)
 26. A pyrophosphate-containing bath for thecyanide-free deposition of copper-tin alloys on substrate surfaces,comprising a reaction product of a secondary monoamine with a diglycidylether, wherein the secondary monoamine is morpholine and the diglycidylether is selected from the group consisting of glycerol diglycidylether, poly(propylene glycol) diglycidyl ether, poly(ethylene glycol)diglycidyl ether and mixtures thereof.
 27. The pyrophosphate-containingbath according to claim 26, wherein the diglycidyl ether is glyceroldiglycidyl ether.
 28. The pyrophosphate-containing bath according toclaim 26, wherein the molar ratio of diglycidyl ether to secondarymonoamine is 0.8 to
 2. 29. The pyrophosphate-containing bath accordingto claim 28, wherein the molar ratio is 0.9 to 1.5.
 30. Thepyrophosphate-containing bath according to claim 26, wherein thereaction product is contained in a concentration of 0.0001 to 20 g/l.31. The pyrophosphate-containing bath according to claim 30, wherein thereaction product is contained in a concentration of 0.001 to 1 g/l. 32.The pyrophosphate-containing bath according to claim 26, furthercomprising an additive selected from the group consisting oforthophosphoric acid, an organic sulfonic acid, boric acid, anantioxidant agent and an organic brightener.
 33. Thepyrophosphate-containing bath according to claim 26, further comprisingN-methylpyrrolidone.
 34. The pyrophosphate-containing bath according toclaim 33, wherein the N-methylpyrrolidone is contained in aconcentration of 0.1 to 50 g/l.
 35. The pyrophosphate-containing bathaccording to claim 34, wherein N-methylpyrrolidone is contained in aconcentration of 0.5 to 15 g/l.
 36. The pyrophosphate-containing bathaccording to claim 26 with a pH value of 3 to
 9. 37. Thepyrophosphate-containing bath according the claim 36 with a pH value of6 to
 8. 38. A method for the galvanic deposition of glossy and evencopper-tin alloy coatings, comprising the introducing of a substrate tobe coated into an aqueous cyanide-free electrolyte bath according toclaim 26 and depositing the copper-tin alloy coating on the substrate.39. The method according to claim 38, wherein the bath is operated at aset current density of 0.01 to 2 A/dm².
 40. The method according toclaim 39, wherein the bath is operated at a set current density of 0.25to 0.75 A/dm².
 41. The method according to claim 38, wherein the bath isoperated at a temperature of 15 to 50° C.
 42. The method according toclaim 38, wherein the bath is operated at a temperature of 20 to 30° C.43. The method according to claim 38, wherein the coatings are depositedon a conductive substrate by means of a rack plating method.
 44. Themethod according to claim 38, wherein membrane anodes are used asanodes.
 45. The reaction product of a secondary monoamine with adiglycidyl ether, wherein the secondary monoamine is morpholine and thediglycidyl ether is selected from the group consisting of glyceroldiglycidyl ether, poly(propylene glycol) diglycidyl ether, poly(ethyleneglycol) diglycidyl ether and mixtures thereof.
 46. The reaction productaccording to claim 45, wherein the diglycidyl ether is glyceroldiglycidyl ether.
 47. The reaction product according to claim 45,wherein the molar ratio of diglycidyl ether to secondary monoamine is0.8 to
 2. 48. The reaction product according to claim 45, wherein themolar ratio is 0.9 to 1.5.
 49. The use of a reaction product accordingto claim 45 as brightener.